CORRELATION OF FORNIX DAMAGE WITH MEMORY IMPAIRMENT IN 6 CASES OF COLLOID CYST REMOVAL

We studied six patients in whom colloid cysts had been removed surgica lly from the third ventricle. The patients were selected simply by ava ilability for the study, not on grounds of clinically diagnosed amnesi a or its absence. The outcomes of operation ranged from one patient wh o had postoperatively resumed a normal life without complaint of memor y disorder at any stage, through four who complained of memory disorde r since operation, to one who was so severely amnesic as to require co nstant supervision. Each patient was given psychometric tests of memor y, and was also scanned by magnetic-resonance imaging. One of us exami ned the six scans and assessed the extent of damage to the fornix, and any other brain damage, in ignorance of the outcomes of the psychomet ric tests. The fornix in the right hemisphere had been destroyed in al l six cases, and all showed evidence of moderate or severe impairment in nonverbal memory. The fornix in the left hemisphere was intact in o nly one patient; this was the patient who had resumed a normal life wi thout complaint of memory disorder. The left fornix was damaged with s ome sparing in one further patient, and the remaining four patients sh owed destruction of the fornix in the left as well as in the right hem isphere. The severity of impair ment in verbal memory in these six cas es was related to the severity of the damage to the left fornix. No ot her evidence of brain damage appeared to be systematically related to memory ability. These results add to the evidence that bilateral forni x damage produces amnesia, and that sparing of the left fornix alone i s sufficient to ensure a more favourable outcome